According to the prior art, multistranded cables are formed by helically winding a plurality of individual steel strands together and in some cable configurations, by helically wrapping one or more layers of strands about one or more central core wires. Multistranded cables formed in this manner include a variety of cross-sectional configurations having differing numbers of layers and differing number of strands in each layer. The different layers may be stranded in different lay directions.
For severe service applications, such as for oil well logging operations and the like, the cable may be enclosed in a protective outer sheath, i.e., an armor jacket which overwraps the cable in a substantially continuous helical manner along the length of the cable. The lay of the armor jacket may be the same or different from the lay of the underlying layer(s) of helically wrapped wire strands. The armor jacket is generally intended to withstand impact damage and corrosive damage generated by moisture- and/or corrosive chemical-laden environments in which the cable is installed, including the severe environment of oil wells or other hostile environments which are typically encountered during oceanographic studies or other naval applications.
It is important that the cable be straight and accurately positioned whether suspended in a relatively narrow bore of an oil well or along the ocean floor. To that end, it is desirable that such cables be manufactured so that they will lay extremely straight when they are unreeled, without twisting, spiraling, casting, or kinking when the cable is unreeled so as to insure accurate placement within the oil well, on the ocean floor or other environment in which the cable is used. In that regard, an important problem in the manufacture of helically wrapped multistranded cables is the undesirable introduction of stresses to the cable during manufacture thereof which are known to cause the cable to twist, spiral and curl up or kink when unreeled. It is believed that the cause of such undesirable effects is the result of inherent stress induced in the strands by reason of friction in the guiding system for the strands during the manufacturing process, resulting in unwanted stresses along the length of the cable. Accordingly, it is important that the multistranded cable be stress relieved prior to use so that it will lay extremely straight when unreeled.
One prior art apparatus 10 for stress relieving multistranded cable is shown in FIGS. 1 and 2. A pay-off reel or supply bobbin 12 for carrying and dispensing a supply of multistranded cable 14 to be stress-relieved is carried on a frame 16 in a standard portal arm shaftless arrangement, the frame 16 being securely mounted to a large motorized turntable 18. The frame 16 includes a pair of frame arms 20 which are adjustably secured to a crossbar 22. The frame arms 20 further include a pair of pintles 24 extending inwardly to secure the pay-off reel 12 in a direction coincident with its axis of rotation. The turntable 18 is constructed with a heavy platform 28 having a diameter exceeding twelve feet for supporting the frame 16 and constructed to carry the weight of the pay-off reel 12 and its supply of cable 14 during operation of the apparatus 10. A large drive motor (not shown) rotates the turntable 18 about a vertical axis A. The drive motor requires a substantial power input necessary to overcome the inertia of the turntable 18 together with the aggregate weight of the frame 16 and the reel 12.
The cable 14 is payed off the pay-off reel 12 in the direction of rotation shown by the arrow and then travels in an upward direction in substantial alignment with the axis of rotation of the turntable 18 to a guide sheave 26. The cable 14 is then advanced in the direction of arrow B over the guide sheave 26 through a strain gage 30 of known design. The cable 14 is further advanced through additional guide sheaves 32, 34, 36 separated one from the next by substantial cable runs and then to a dual wheel capstan 38 separated from guide sheave 36 by another substantial cable run. The advancing cable 14 is carried through multiple grooves formed in each wheel 40, 42 of the capstan 38 with a predetermined tension to stress relieve the advancing cable 14, which is then coiled onto take-up reel 44 mounted for rotation in a stationery portal-arm take-up stand 46 similar to that mounted to the turntable 18. This final cable run is likewise of a substantial length.
In operation, the rotational speed of the pay-off reel 12 is controlled to rotate at relatively slow angular speeds not exceeding fifty revolutions per minute during which time the tension at the take-up stand 46 is controlled to direct the advancing cable 14 through the capstan 38 to relieve stresses in the cable 14. This operating speed restriction is made necessary due to the heavyweight of the pay-off reel 12 and turntable 18 resulting in undesirable high energy input and maintenance requirements. Another important problem with this prior art apparatus is the plurality of relatively long cable runs between the various guide sheaves, capstan 38 and take-up stand 46, which cable runs require extended operating space necessary to complete the cable strain relief process.